Systematics of Bangia (Rhodophyta) in North America. I. Biogeographic trends in morphology

Abstract

A total of eight species of Bangia have been recognized from North America but only one or two are presently included in taxonomic works. To clarify the systematics of this genus, 84 sites were sampled throughout its range, including south-east Alaska to the Baja Peninsula, Newfoundland to northern Georgia and Lake Michigan to Lake Ontario. Filament length and pigmentation proved to be of little value in differentiating populations. In contrast, significant differences were found when filament diameters were grouped according to the basin from which the samples were collected (P < 0. 001). The mean in situ diameters of monospore releasing filaments from the Pacific, Atlantic and Great Lakes were 157, 91.6 and 75.3 μm, respectively. Similar size differentials were observed for male and female plants in the field. In addition, growth in culture under controlled or varied conditions resulted in a similar trend of basin-based differences in filament diameters for asexual germlings, mature asexual plants or conchocelis filaments. The asexual monospore-releasing plants had average diameters remarkably similar to those of field-collected plants: 163, 91.6 and 74.4 μm for Pacific, Atlantic and Great Lakes filaments, respectively. At least five populations were sampled at each of the type localities of B. enteromorphoides Dawson, B. maxima Gardner and B. vermicularis Harvey. There appears to be no basis for continuing to recognize these populations as being separate from those of the rest of the Pacific. In summary, there are minimally two species of Bangia in North America, representing the populations of the Atlantic (B. atropurpurea (Roth) C. Ag.) and the Pacific (B. vermicularis). The small size of the Great Lakes plants may indicate incipient speciation and hence a new variety may be warranted.